1. Field of the Invention
The present invention relates to an ammonia gas sensor for detecting ammonia gas contained in a gas under measurement.
2. Description of the Related Art
An ammonia gas sensor is disclosed in Patent Document 1. This ammonia gas concentration measurement apparatus includes a solid electrolyte member, a reference electrode provided on one side of the solid electrolyte member, and a detection electrode provided on the opposite side of the solid electrolyte member.
When in use, the reference electrode is exposed to the atmosphere, and the detection electrode is exposed to a gas under measurement. The ammonia gas concentration measurement apparatus generates an electromotive force that is proportional to an electromotive force between the reference electrode and the detection electrode. This in turn depends on the concentration of ammonia gas in the gas under measurement, to thereby detect the concentration of the ammonia gas.
[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. 2003-83933
3. Problems to be Solved by the Invention
In the ammonia gas concentration measurement apparatus of Patent Document 1, a detection lead is formed to extend from the detection electrode. However, a portion of the detection lead is also exposed to the gas under measurement together with the detection electrode. Since the detection lead is formed of an electrically conductive material such as a noble metal, an electromotive force may be produced between the detection lead and the reference electrode due to ammonia gas in the gas under measurement. As a result, the difference in electromotive force attributable to the detection lead can change the electromotive force thus generated, and may lower accuracy in detecting the concentration of ammonia gas.